In the field of semiconductor, the non-volatile memory has been widely employed in a large number of electronic products, including digital camera memories, cellular phones, and personal computers, due to its ability of retaining the stored data even when not powered, its small volume and low power consumption, and its reusability. In a typical non-volatile memory, an element having a control gate made of a polysilicon material and a silicon-oxide-nitride-oxide-silicon (SONOS) structure is used as a control element for controlling data write-in via channel-hot-electron injection and data-erase via hot hole injection. The layers of the SONOS structure are sequentially stacked on a silicon substrate, and the nitride layer sandwiched between the upper and lower oxide layers is used as a source of charge trapping. The upper and lower oxide layers are used as an isolating layer and a tunneling layer, respectively. In the SONOS structure, the oxide-nitride-oxide (ONO) structure may be used to replace a floating gate to effectively reduce the use of masks in the manufacturing process of non-volatile memory and to reduce the size of the memory.
In the gate structure for the non-volatile memory cell, in order to reduce the sheet resistance of the polysilicon gate and the resistance values between the gate and other contacts, a metal layer would usually be further formed on the polysilicon gate to improve the relatively high resistance value of the polysilicon gate. Conventionally, a tungsten metal layer is deposited on the polysilicon gate to achieve the above-mentioned purpose. For example, Taiwan Patent Publication Number I287834 discloses a technique for further forming a tungsten metal layer on the polysilicon gate. However, the tungsten metal layer used as a cap layer on the polysilicon gate is easily subject to deterioration and involves complicated procedures to form it. After the tungsten metal layer is deposited, it must be quickly capped using the nitride layer to avoid the deterioration thereof. Meanwhile, to remove the capping nitride layer from the tungsten metal layer, masks must be used in the etching process in order to form the polysilicon gate and other patterns. Therefore, the conventional way of forming the tungsten metal layer on the polysilicon gate is uneconomical for use when the simplification of manufacturing process and the reduction of manufacturing cost of the non-volatile memory are considered.
It is therefore tried by the inventor to eliminate the drawbacks in the conventional way of manufacturing the gate for the non-volatile memory cell by providing an improved non-volatile memory cell manufacturing method, in which a self-aligned metal silicide layer is used to replace the conventional tungsten metal layer, so as to effectively avoid the problem of a deteriorated tungsten metal layer due to subsequent high-temperature tempering process, omit the use of marks in the etching process for forming the polysilicon gate, and accordingly, achieve the purpose of simplifying the etching process and reducing the manufacturing cost of the non-volatile memory cell.